This invention relates generally to geothermal power control systems and more particularly to a process encompassing the utilization of all energy resources available from a geopressured geothermal reservoir for the production of electric power and pipeline quality gas and the production and injection of engineered fluids for water and/or miscible flooding of depleted petroleum reservoirs.
Economic production of oil from an underground formation becomes impossible when the reservoir pressure drops below a certain level. When that occurs, it has been the practice to employ one or more methods of secondary and tertiary oil recovery. These methods require a new driving force to displace oil from the underground formations toward adjacent production wells in the same field.
Secondary and tertiary oil recovery techniques have centered upon engineered floods of natural gas, CO.sub.2, water, and polymer aqueous solutions for the purpose of (1) physically changing the properties of oil (density, viscosity, surface tension and wetting characteristics), and (2) uniformly sweeping it through the reservoir. Compared with water flooding, miscible flooding is the more sophisticated technique for oil displacement. The oil is diluted with natural gas, CO.sub.2 or other light hydrocarbons in order to reduce the viscosity and to increase the mobility of the oil. The relatively more expensive gas is usually followed by a mixture of water and surfactant (detergent, ammonia, etc.). A diffusion front (oil saturation bank) is caused by the first soluble material and formed near the injection well. Remaining oil droplets are mobilized by the surfactant and water to complete the oil bank that sweeps the remaining reservoir oil through the rock to production wells. At the end, polymerized water (micellar polymer) with high viscosity, and the ability to maintain a stable and uniform flood front, is pumped into the injection well as a sweep or displacement mechanism. Performance of the system will increase when all these fluids are heated because the miscible phase is more soluble, the fluid viscosities are reduced and the surfactant has better cleaning or wetting properties.
Instead of pumping the fluids to displace oil from reservoir rocks, it is more economical to use the hydraulic energy available in a geopressured aquifer. These concepts have centered upon using hot brine as a motive force behind the engineered fluids. Geopressured wells of commercial productivity (i.e., 10,000-40,000 BPD for ten years) are not likely to be found in strata productive of oil and gas. These strata are usually highly faulted producing small structural traps. In productive areas, wells are often drilled to great depths in search of additional oil and gas only to locate water saturated sands. That happens more often than not. But during the life of the productive field one can expect a deeper test and it will almost certainly reveal some geopressured brine zone that has more than enough fluid under pressure to sweep an existing pressure depleted hydrocarbon field.
In most cases, artificial floods are composed of engineered fluids of specified compositions and injected at controlled rates. The objective is to design a general process for enhanced oil recovery utilizing the hydraulic and thermal energy of geopressured geothermal brine resources as a means for offsetting the cost of the water flood. The invention described in U.S. Pat. No. 4,484,446 by the present inventor was made in satisfaction of the objective of converting thermal and hydraulic energy to electric power in the most thermally efficient manner possible.
Another objective for the exploitation of geopressured geothermal energy resource fluids is to be seen in the shortage of natural gas in recent years. Brine is typically saturated with natural gas in quantities of from thirty to fifty standard cubic feet per barrel (5.34-8.91 m.sup.3 gas/m.sup.3 brine) at 250.degree. F. to 450.degree. F. (395 K to 505 K). The large extent of that resource has prompted various estimates of recoverable gas reserves that could extend the U.S. reserve life index from five to two hundred years. The present invention addresses the need to recover fluids for gas and water floods, and to recover natural gas, as well as the utilization of hydraulic and thermal energy.